1. Field of the Invention:
This invention relates to electrical resistors and more particularly to resistor units for use in motor starters or other electric apparatus which are exposed to heavy shock forces.
2. Description of the Prior Art:
Electric resistor units of the type disclosed in U.S. Pat. Nos. 1,550,641, 2,249,474, and Re. No. 22,313 disclosed resistance conductors of the ribbon type wound helically on refractory insulators which in turn are supported on elongated metal straps. When these assemblies are subjected to high impact shock, or low frequency vibration due to jogging during road shipment, or in low frequency vibration in use due to adjacent machinery, the straps tend to sag and thereby crack the ceramic insulators.
Various attempts to overcome that problem have been made, such as the resistance unit shown in U.S. Pat. No. 2,390,790, in which a plurality of insulators are mounted on a support strap in end-to-end abutment with rounded end surfaces to impart a rolling action of abutting end surfaces of adjacent insulators when the support straps bend. However, the straps bend or flex horizontally in response to heavy shock forces such as occur on naval vessels when the guns are fired.
Associated with the foregoing has been a problem of providing a suitable fastening means for mounting the refractory insulators on the support strap in a fool-proof manner. A recurring difficulty of fastening means of prior construction has been the failure of metal fastening means due to overheating in normal use.